My first job I left, I actually FLEW to my boss's office (actually, my boss's boss, but the guy who hired me and who I felt I should tell the news to). I later went back to that company, so it was a case of "you reap what you sow". I've never done that again, but I've always done it in person. Always a minimum of two weeks, always accompanied by a written letter of resignation.
Except the one time I was let go, in which case I went back to my office, packed my shit, handed my computer and phone to my suddenly ex-boss and walked out. I later heard he was pissed he didn't get two weeks from me, and I clearly burned a bridge with that move not only with my direct boss, but his boss (the guy I once flew to see) but I can sleep at night.